1. Technical Field of the Invention
The present invention relates generally to a fail-safe air induction control apparatus for automotive engines designed to control the position of a throttle valve electrically using an actuator such as an electric motor, and more particularly to a simple structure of such an air induction apparatus which is capable of holding a throttle valve at a partially opened position accurately in the event of a failure of an actuator.
2. Background Art
In recent years, air induction control apparatuses for automotive engines called electronic throttle systems become used which actuate an electric motor as a function of a pedal stroke operated by a vehicle driver to control the position of a throttle valve. The air induction control apparatus is designed to supply the current to the electric motor in response to a signal from a pedal position sensor which indicates the position of an accelerator pedal and turn the throttle valve through the motor, thereby adjusting the quantity of air entering the engine.
Some of the air induction control apparatuses are designed to hold a middle hold position between a fully closed and a fully opened position using a fail-safe mechanism consisting of a plurality of springs for enabling the vehicle to run in an emergency running mode if the supply of current to the electric motor is cut for some cause.
For example, Japanese Patent First Publication No. 3-271528 discloses an electronic throttle system equipped with a fail-safe mechanism. FIG. 7 shows such a fail-safe mechanism schematically which is designed to hold a throttle valve 13 through a throttle shaft 12 at a middle hold position between a fully opened an a fully closed position within an intake air passage 11 in the event of a failure in supplying an electric motor 20.
The fail-safe mechanism consists of an opener lever 21 moved together with the throttle shaft 12 by the electric motor 20, a middle position hold stopper 14, a fully closed position stopper 15, a middle position hold movable lever 22, a first spring 23 urging the opener lever 21 and the movable lever 22 into engagement with each other, and a second spring 24 urging the movable lever 22 in a direction of closing the throttle valve 13 into engagement with the middle position hold stopper 14. A fully opened position stopper defining the fully opened position of the throttle valve 13 is omitted for convenience of illustration.
In operation, when the electronic throttle system is in service, and it is required to open the throttle valve 13 from the middle hold position, the electronic motor 20 is rotated in a valve-opening direction against the spring pressure exerted by the second spring 24. Conversely, when it is required to close the throttle valve 13 from the middle hold position, the electronic motor 20 is rotated in a valve-closing direction against the first spring 23. If the supply of current to the electric motor 20 is cut for some cause, so that the electric motor 20 outputs no torque, the first and second springs 24 and 23 serve to keep the movable lever 22 in contact with the middle position hold stopper 14, thereby holding the throttle valve 13 at the middle hold position through the opener lever 21. Specifically, a complex mechanism consisting of the opener lever 21, the movable lever 22, and the first and second springs 23 and 24 is used to hold the throttle valve 13 at the middle hold position in the event of a failure in operating the electric motor 20, thus resulting in an increase in manufacturing cost. Additionally, the movable lever 22 is so constructed as to define the middle hold position through engagement with the opener lever 21. Thus, small dimensional errors of the movable lever 22 and/or the opener lever 21 will result in an undesirable shift of the middle hold position.
It is therefore a principal object of the invention to avoid the disadvantages of the prior art.
It is another object of the invention to provide a simple structure of an air induction apparatus for automotive engines which is capable of holding a throttle valve at a partially opened position accurately in the event of a failure of an actuator.
According to one aspect of the invention, there is provided an air induction control apparatus for an internal combustion engine which is equipped with a fail-safe valve control mechanism. The air induction control apparatus comprises: (a) a throttle valve supported by a throttle shaft rotatably within an intake air passage to control the quantity of intake air flowing through the intake air passage; (b) an actuator working to produces an output which rotates the throttle shaft for opening and closing the throttle valve selectively between a fully closed portion and a fully opened position; (c) a first stopper defining a middle position at which the throttle valve is held between the fully opened and closed positions when the actuator outputs no torque; (d) an opener member connected to the throttle shaft to be rotatable together with the throttle shaft; (e) a first spring winding; and a second spring winding (f). The first spring winding is disposed so as to exert a first spring pressure on the opener member in a first rotational direction in which the throttle valve is rotated from the fully opened position to the middle position. When the actuator produces no output, the first spring winding is urged at an end thereof into constant engagement with the first stopper to hold the opener member from rotating in a second rotational direction in which the throttle valve is rotated from the fully closed position to the middle position. The second spring winding has a first and a second end between which the opener member extends. When the actuator produces no output, the first end abuts against a second stopper, the second end abuts against the opener member so as to exert a second spring pressure on the opener member in the second rotational direction to nip the opener member between the second end of the second spring winding and the end of the first spring winding elastically through the first and second spring pressures, thereby holding the throttle valve at the middle position.
In the preferred mode of the invention, the first and second stoppers may be formed by a one-piece member having a plane against which the end of the first spring winding and the first end of the second spring winding abut.
The first and second stoppers have surfaces rounded so as to establish a point contact with the end of the first spring winding and the first end of the second spring winding, respectively.
A middle position adjusting mechanism may further be provided which is designed to shift a contact of the end of the first spring winding with the first stopper in one of the first and second rotational directions to adjust the middle position to a desired one.
A spring holder may further be provided which works to hold the end of the first spring winding and the first end of the second spring winding from shifting out of engagement with the first and second stoppers. The spring holder may be implemented by pins installed on the opener lever.
The second winding provides an elastic nip to the opener member through the first and second ends of the second winding within a range in which the throttle valve is rotated from the fully opened position to the middle position.
Each of the first and second spring windings is made of a coil spring having a given length extending parallel to the throttle shaft.
The first and second spring windings may be wound in alignment with each other around a shaft extending parallel to the throttle shaft.
The first and second spring windings may be wound in alignment with each other around a shaft extending in alignment with the throttle shaft.
The first and second stoppers may be implemented by a one-piece member formed on a throttle body. The end of the first spring winding and the first end of the second spring winding are joined to each other to form a connection. The connection is urged into constant engagement with the one-piece member when the actuator outputs no torque.
According to another aspect of the invention, there is provided an air induction control apparatus for an internal combustion engine. The air induction control apparatus comprises: (a) a throttle valve supported by a throttle shaft rotatably within an intake air passage to control the quantity of intake air flowing through the intake air passage; (b) an actuator working to produce an output which rotates the throttle shaft for opening and closing the throttle valve selectively between a fully closed portion and a fully opened position; (c) a middle position hold stopper defining a middle position at which the throttle valve is held between the fully opened and closed positions when the actuator outputs no torque; (d) an opener member connected to the throttle shaft to be rotatable together with the throttle shaft; and (e) a spring made up of a first and a second winding and a third spring portion formed by a connection of the first and second windings. An end of the first winding opposite the third spring portion engages a stopper formed on a throttle body so as to produce a first spring pressure which urges the third spring portion in a first rotational direction in which the throttle valve is rotated from the fully opened position to the middle position. An end of the second winding opposite the third spring portion engages the opener member so as to produce a second spring pressure which urges the opener member in a second rotational direction in which the throttle valve is rotated from the fully closed position to the middle position. When the actuator produces no output, the third spring portion is held in engagement with the middle position hold stopper to nip the opener member between the third spring portion and the end of the second winding elastically through the first and second spring pressures, thereby holding the throttle valve at the middle position.
In the preferred mode of the invention, the middle position hold stopper has a surface rounded to establish a point contact with the third spring portion of the spring.
A middle position adjusting mechanism may further be provided which is designed to shift a contact of the third spring portion of the spring with the middle position hold stopper in one of the first and second rotational directions to adjust the middle position to a desired one.
A spring holder may further be provided which works to hold the third spring portion of the spring from moving out of engagement with the middle position hold stopper.
The spring holder may be implemented by pins installed on the opener lever.
The second winding provides an elastic nip to the opener member through the third spring portion and the end of the second winding within a range in which the throttle valve is rotated from the fully opened position to the middle position.
The spring may be made of a coil spring having a given length extending parallel to the throttle shaft. The coil spring may be wound around a shaft extending parallel to the throttle shaft. The coil spring may alternatively be wound around a shaft extending in alignment with the throttle shaft.